A large proportion of persons living with HIV infection (PLH) in Russia are not presently in HIV medical care and a majority of PLH on antiretroviral therapy (ART) do not adhere to their regimens at levels needed to achieve full viral suppression. This results in poor health outcomes. Because viral suppression reduces the likelihood of HIV transmission, poor care attendance and ART adherence also increase HIV disease incidence at a population level. This application proposes to expand a longstanding, bilateral, and interdisciplinary collaboration between investigators at the Center for AIDS Intervention Research (CAIR) at the Medical College of Wisconsin, USA and a scientific team at St. Petersburg State University Medical Faculty to develop and pilot test a novel intervention that harnesses peer social support to improve ART care engagement and adherence. In the first year qualitative phase, the scientific team will carry out and analyze data from in-depth interviews with approximately 60 PLH and key informants knowledgeable about the PLH community. The sample will include PLH in and out of medical care, selected to represent diverse exposure risks including drug users, men who have sex with men, and heterosexual PLH. The qualitative phase will identify individual-level, social, and structural factors responsibe for poor treatment attendance and adherence as well as resources that facilitate medical care, especially the role of social support. Phase II of the research will integrate qualitative findings into a peer social support intervention designed to improve care engagement and ART adherence. Our prior research has established that PLH in the community are often clustered in their friendship groups with other HIV+ persons and that these intact PLH friendship groups can be recruited into research. The intervention to be tested differs from traditional one-on-one adherence patient counseling by intervening with entire PLH friendship groups to create peer social and normative support for treatment. The test-of-concept pilot intervention will recruit 20 out-of-care or ART nonadherent seeds and also all willing HIV+ persons in each seed's personal friendship group (expected n=100 participants). Following baseline assessment of care engagement, ART adherence, psychosocial distress, substance use, and CD4+ and viral load, 10 of the PLH friend groups (n=50 participants) will be randomized to an intervention condition and 10 PLH friend groups (n=50) to the comparison condition. All members of each friendship group in the intervention condition will together attend a 7-session intervention that targets attitudes, intentions, and skills for entering, remaining, and adhering to HIV medical care. Because participants will attend sessions with other PLH who are their own friends in day-to-day life, all sessions will build and increase mutual social support within each friendship group for care and adherence. Intervention outcomes will be determined by baseline to 6-month followup change on behavioral and biological measures. If the intervention pilot test provides evidence of intervention benefit, we will later propose a larger scale trial of the approach.